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Is it possible to coarsen the mesh?

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Old   July 29, 2017, 19:01
Default Is it possible to coarsen the mesh?
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Charlie
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Hi foamers,

I know it's a bit silly to ask this, but it's interesting that we are all discussing how to refine the mesh in the whole domain or regions of interest, however, I wonder if it's possible to coarsen the mesh in certain regions.

This question is especially relevant when we have irregular shape (for example, cylinder, stars, etc) in the domain or along the boundary. We could certainly initialize the region to be coarse and then use refineMesh or snappyHexMesh to obtain a finer mesh. However, the initial shape or BC will be distorted because of the coarse mesh at the first step. So my idea is to use fine mesh initially, and then coarsen the mesh in regions far away from the irregular shape or BC, is this possible? Could you let me know which tool is useful for this purpose?

Another idea is to create blocks of different mesh resolutions, but this will be problematic, as blockMesh doesn't know how to connect faces with different number of meshes, I tried to use mergePatchPairs, but this will create two internal patches, which doesn't make sense, because these internal patches act like a boundary patch, and the numerical results are affected by them.

Any suggestions?

Best

Charlie
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Old   July 30, 2017, 05:44
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Bravo to Charlie, yeah it's silly but some people have an habbit to take flying arrow in their ass people like Me, You, Issac Newton.. Let's come to the point well you can set the Mesh coarse, Fine apple, orange anything in ICEM CFD and export it as openfoam format.

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Old   August 2, 2017, 22:02
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Thank you, Nishant, I guess there are a lot of meshing tools out there, like ICEM CFD, gmesh, salome, cfmesh, etc. I've tried a few, and they all have their own pros and cons. I guess, I will invest more time on them when I have a very complicated geometry.
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Old   August 2, 2017, 22:24
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Roger that Charlie, please send me the image of complicated geometry. May be I will provide some reinforcement to you.

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Old   August 2, 2017, 22:59
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Hi Charlie,

Quote:
Another idea is to create blocks of different mesh resolutions, but this will be problematic, as blockMesh doesn't know how to connect faces with different number of meshes, I tried to use mergePatchPairs, but this will create two internal patches, which doesn't make sense, because these internal patches act like a boundary patch, and the numerical results are affected by them.
Yes, this can be done. Mesh them individually, put them all together using mergeMeshes & connect the faces/patches that have different mesh resolution using cyclicAMI. I would not suggest using blockMesh's mergePatchPairs or stitchMesh as they usually are unable to do multiple ones.

Hope this helps.

Cheers,
Antimony
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